The present invention relates to an improved pumping unit drive system for pumping fluids such as oil from an underground level to ground level.
A wide variety of pumping units are used to raise fluids such as oil to a recovery level which is typically at or near ground level. One commonly used approach is a mechanical pumping jack which uses a motor to drive a tilting beam mechanically such that the beam oscillates, thereby driving a ram alternately upwardly and downwardly to power a down hole pump. Typically, the tilting beam is provided with counterweights to reduce the load imposed on the motor.
A second approach is to utilize a motor to pressurize hydraulic fluid which operates a cylinder to alternately raise and lower the ram attached to the down hole pump. In many applications of such hydraulic drive systems, the hydraulic fluid pressurized by the motor is used both to lift the entire weight of the ram as the ram is moved upwardly and to lift less than the entire weight of the ram as the ram is allowed to move downwardly. Depending upon the depth of the well, the weight of the ram can vary considerably, and relatively high pressure hydraulic systems are often required to oscillate the ram with these prior hydraulic drive systems.